The inventions relate generally to clock recovery, and more specifically to program clock reference (PCR) clock recovery in an internet protocol (IP) network. The inventions apply even more generally to audio and video time management, clock control and display clock control. PCR clock recovery is an important component enabling a decoder clock to be synchronized with the encoder clock in a point to multipoint broadcast network.
In point-to-multipoint communication systems, an IP network supports bidirectional data communication between a central entity and multiple customer premises equipment (CPE). Example point-to-multipoint communication systems include cable modem systems, fixed wireless systems, and satellite communication systems. In each system, the communication path from the central entity to the CPE is typically referred to as the downstream, while the communication path from the CPE to the central entity is typically referred to as the upstream. A CPE may be a cable modem, a settop box, or a cable gateway, to provide some examples.
Audio-visual information may be transferred in an IP network in accordance with any of a variety of standards, such as the International Organization for Standardization/International Electrotechnical Commission 13818-1 International Standard, published on Nov. 13, 1994 (the ISO/IEC 13818 standard). This standard is consistent with MPEG2. The central entity of the point-to-multipoint communication system generates a program clock reference (PCR) clock in accordance with the standard and transmits the audio-visual information based on the PCR clock. The CPE(s) traditionally processes the audio-visual information for display using the PCR clock. However, audio-video information in IP networks often exhibits relatively large and irregular propagation delays, hindering the CPE(s) from adequately recovering the PCR clock. Moreover, PCR timestamps may not be sufficiently reliable for PCR clock recovery.
What is needed, therefore, is a system and method that addresses one or more of the aforementioned shortcomings of conventional PCR clock recovery techniques.
In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears.